1. Field of the Invention
The present invention relates to a process cartridge having a plurality of developing units using different color toners and being detachable from the body of an image forming apparatus, and an image forming apparatus using such a process cartridge.
2. Description of Related Art
A well-known type of image forming apparatus can output a high-quality image by replacing a process cartridge including an electrophotographic photoconductive member and a developing unit with another cartridge even if toner in the developing unit runs out.
A process cartridge having a plurality of developing units is disclosed in U.S. Pat. No. 4,500,195.
In order to know when it is necessary to replace the process cartridge, it is preferable to provide a means for detecting whether the amount of toner in each developing unit falls below a predetermined amount. Thus, a signal generating member for generating an electric signal in accordance with the amount of remaining toner is also mounted in the developing unit.
However, if a discriminating circuit is mounted in each developing unit so as to discriminate, based on the output of the signal generating member, whether the amount of the toner remaining in the developing unit is above a predetermined amount, the construction of the image forming apparatus becomes complicated and its size is enlarged.
Thus, it is preferable from the point of view of reducing the cost of the process cartridge to mount the above discriminating circuit in the body of the image forming apparatus rather than int he process cartridge.
However, if an output terminal for transmitting a signal from the signal generating member to the discriminating circuit in the apparatus body is disposed in each developing unit in the process cartridge when the process cartridge is attached to the apparatus body, it is necessary to mount a plurality of input terminals to engage the output terminals in the apparatus body. Therefore, the number of the output and input terminals becomes large, thereby increasing the rate of damage and contact failure of these terminals when the process cartridge is attached to the image forming apparatus.